1. Field of the Invention
The present invention relates to a method and a device for distinguishing between and performing fault processing on transmission line faults and secondary faults generated by the effect of transmission line fault events in transmission systems comprising a plurality of transmission devices (nodes) and transmission lines connecting them.
2. Description of the Related Art
When a fault occurs in a transmission system comprising a plurality of transmission devices (nodes) and transmission lines connecting them, a higher level alarm is generated in response to the fault; depending on the fault, secondary alarms may be generated due to the effects of the upper level alarm.
For this reason, priority is established among alarms, and when a higher level alarm is generated, an alarm suppression process for suppressing generation of lower level alarms is carried out.
However, faults generated on transmission lines can only be detected by nodes connected to the transmission line on which the fault has occurred, and other nodes cannot recognize the transmission line fault that is the primary cause, detecting only lower level alarms. For example, in the ring connection system depicted in FIG. 2, when a fault is generated on the transmission line between node #1 and node #2, node #1 and node #4 detect an inter-nodal transmission fault. Node #2 detects an input signal interrupt fault, an inter-nodal transmission fault, and abnormal connection path parity between terminal A and terminal a. Node #3 detects inter-nodal transmission fault, an abnormal connection path parity between terminal B and terminal b, and an abnormal connection path parity between terminal C and terminal c.
As a result, the network supervisory device is notified by a plurality of alarms, all originating in the same fault, from the transmission devices. This leads to increased traffic and to difficulty in identifying the primary cause.
Lower level alarms take various forms, such as those generated unconditionally and those generated only in relation to transmissions through a transmission line on which a fault has occurred.
Thus, in addition to suppression of alarm generation in the nodes themselves, means are required to suppress inter-nodal alarms generated when an alarm is generated on a transmission line.
In order to suppress such inter-nodal alarms, the following two technologies, for example, are used conventionally.
The first conventional technology involves detection of alarm data by a supervisory program loaded on each node; when higher level alarm transmission line fault data is detected, this data is transmitted to other nodes, and the nodes receiving this transmission ignore lower level alarm events and do not notify the network supervisory device.
The second conventional technology involves input of all alarm data by the network supervisory device, after which the alarm data is retrieved one item at a time, and if a higher level alarm occurs, the lower level alarms are ignored and are not retrieved.
With the first conventional technology, there is a drawback in that lower alarms notification is made until the higher level alarm failure data has been transmitted to all nodes and a drawback in that rapid processing is not possible due to the fact that transmission line fault data is transmitted by the agency of the supervisory program loaded on each node.
With the second conventional technology, there is a drawback in that the network supervisory device is notified of all occurring alarms so traffic on transmission lines increases to produce a jam, and a drawback in that the burden on the network supervisory device increases.